Electric heater.



No. 816,172. PATENTED MAR. 27, 1906. H, N. MORSE & J. G. W. FRAZER.

ELECTRIC HEATER. APPLIOATIOH FILED APR. 18. 1905.

37 Mom fi V focwe Hagar UNITED STATES PATENT OFFHJE.

'HARMON N. MORSE AND JOSEPH C. W. FRAZER, OF BALTIMORE, MARY- LAND, ASSIGNORS OF ONE-THIRD TO ROBERT B.

MORE, MARYLAND.

MORSE, BALTI- ELEOTRIO HEATER.

Specification of Letters Patent. 7

Application filed April 18, 1905. Serial Ho. 256,229.

Patented use 27, 1906.

more and State of Maryland, have invented certain new and useful Improvements in Electric Heaters, of which the following is a specification.

The object of our invention is to provide an electric heater of an improved construction which may be cheaply manufactured, will efiiciently convert electricity .into sensible heat, and will be strong and durable, standing Wear, as well as being easily adapted to the use of electric currents whose voltage varies within wide limits.

We have found that if a slab of soapstone be spread with a thin layer of graphite a fairly good resistance element for an electric, heater may be obtained. Soapstone is usually the best material to form the base or support for the resistance medium, because it is easily cut to the desired shape, its surface can be made very smooth, which is essential to the best results, and it withstands better than any other available non-conducting material great and sudden changes in temperature. Graphite not only conducts electricity, but its conductivity increases with rising temperature, and when applied the thin layer provides the desired resistance to produce eat. While we have specified that soapstone is the preferred material for the base, we wish it understood that so far as part of our invention is concerned porcelain, terracotta, and other materials may be used for the non-conducting base.

If dry aphite be rubbed upon the smooth surface 0 soapstone or like material, a suiiiciently thick or heavy coating cannot be obtained to conduct the requisite amount of current. A thicker covering of graphite may be obtained by repeated applications of it in a wet condition with a flat camels-hair brush. The surface to which it is applied must, however, be hot enough to evaporate the water almost instantaneously; otherwise the deposit will be quite uneven; but although a sufliciently thick coating may be thus obtained the results arenotsatisfactory, as the material lacks adhesiveness, and when an attempt is made to harden it by polishing with a stiff brush much of the graphite is detached, and the surface which is produced is easily mpn'ed by handling or by contact with 'other ob ects. We have discovered that if we run: with aphite a suitable quantity of washed and olted clay and make a thin paste of the mixture with water a suitable substance is obtained which may be applied to a smooth surface like that of soapstone, which adhere thereto, which may be polished, and which will be durable and in every way eflicient. We have also found that the addition of a little soap gives even better results, and also that such a paste may be a plied with good results to other noncon ucting substances, such as porcelain, terra-cotta, &c.

In carrying out our invention we mix gra hite and clay and sometimes a little soap wit water, as above described, in proper proportions to obtain a thin paint or paste. We then by means-of-a camels-hair brush coat the smooth surface of a block or slab of soapstone oi other non-conducting base with the paste while the base is bein heated, so that the water of the paste wil be quickly evaporated. After the slab is thus coated the graphite-surface is vigorously polished with a stiff brush, and subsequent coatings may be applied and polished in the same way. The several coatings, with the intermediate polishings, are made for the purpose of increasing the conductivity of the heater to the desired degree to carry the amount of current necessary to obtain a good heat. After thefirst application and polishing the resistance of the coating is so high that very little current can pass, and therefore little heat is produced; but by repeated coatings and polishings the conductivity of the heater may be increased until the requisite resistance is obtained to permit the passage of the desired amount of current.

In the drawings, Figure 1 is a pers ective view of an electric heater constructe in accordance with our invention. Fig. 2 is a pers ective view of the slab or piece of non-conucting material before it is coated. Fig. 3 is a perspective view of one of the plates employed for attaching the circuit-wires. Fig. 4 illustrates the manner in which the nonconducting base is heated while the coating is being applied. Fig. 5 is a perspective view showing a modification of our invention in which the slabs are arranged vertically in pairs and electrically connected with each other. Fig. 6 is a perspective view of a heater in which the non-conducting base is in the form of a tube.

Referring to Figs. 1 to 5, inclusive, it may be assumed that the slab or block A, as before stated, is preferably of soapstone, although porcelam or some other materials would be suitable in some cases. The metal plates B are applied to the ends of the slab and secured thereto by bolts C, the circuitwires D being connected with the bolts as illustrated; Preferably the top, bottom, and two sides of the slab are covered with the graphite mixture, the surfaces to which the mixture is applied being made perfectly smooth in order that the coating may be of absolutely uniform thickness. In applying the coating the plates B first have their inner surfaces covered with the mixture of graphite and clay, and those portions of the soapstone which are afterward covered by the plates are evenly spread with a rather thick ayer of the paste. The plates are then bolted to the stone in the manner indicated in Fig. l. The circuit-wires D are connected with an electric circuit, including an ammeter. Then the slab is heated by means of a lamp or other heater, a board of asbestos E being preferably inter osed between the lamp and the slab. en the stone is hot enough to evaporate water with rapidity, but without sputtering, the paste, much thinned with water, is evenly applied with a flat camel s-hair brush whose width is referably about twent -five millimeters. The whole surface shou d be covered each time; but the brush should not pass more than once over any ones 0t during each application. After each app 'cation the surface is vigorously polished-with a stifl brush, such as a toothbrush.

An even distribution of the graphite is of great importance, for if it is unevenly distributed the resistance in different regions will vary and more heat will be developed at some points than at others and. the graphite will burn out in certain spots, while the whole aniohnt of heat developed is much less than the surface ought to bear with safety.

I .oe rras the conductivity of the graphite covering is in creased to a point where the current suffices to maintain the proper temperature the block is removed from the asbestos-board and its surface is carefully explored with a voltmeter with reference to the uniformity of the distribution of resistance. The subsequent applications of the graphite mixture are regulated with a view to securing uniform conductivity over the whole surface-that is, those spots which are found by the voltmeter to exhibit a higher resistance are painted more thickly than they were before. With care it is easy to prepare a heater in a short time on which the graphite is very evenly distributed and so firmly adhered that it will not visibly soil the fingers in handling. If as the painting proceeds the surface becomes so hot that the water is evjafporated with explosive violence and the s ace presents a spotted appearance, owing to an uneven s reading of material, the circuit should be roken and the stone allowed to cool before making another application of the paint.

The thickness of the graphite coating should be regulated with a view to the most economical expenditure of energy in the subsequent use of the heaterin other words, with a view to dispensing with as much as possible of the external resistance which is l always inserted in the circuit for the purpose of regulatin the temperature where the heater is usefor instance, in an air-bath.

The clay used with the graphite is employed not only as a binder, but as a spreading agent. It produces with the graphite a finely divided homogeneous mixture and makes it easy to give a uniform distribution over the surface to which the paste is applied, so that the resistance may be equal at all points and a fine polish can be obtained, presenting a hard smooth surface not easily injured, and yet the coating may be thick enough to obtain the re uislte conductivity, but is not so thick that 1t is apt to flake ofi. A high temperature can also be obtained 'when clay is employed with graphite, be-

cause clay does not lose its water until the tem erature has reached about 425 centigra e. A constant temperature of, say, about 400 centigrade may be used for a long time without injuring the coating.

Any suitable soa may be mixed with the graphite, clay, an water. Preferably we use only a small quantity of concentrated so- :lution of soap, which decomposes at 350 centigrade.

The proportions of graphite and clay or graphite, clay, and soap may be easily deter- I mined by experience. The proportions cannot be rigidly adhered to in preparing the coating mixture, because experience has shown that it is necessary to vary the percentage of the ingredients considerably, according to the quality of graphite and the nature of the clay used in order to secure a mixture which will have the necessary spreading, polishing, hardening, and adhering qualities. The following pro ortions have been found to Work well: grap 'te, 54.8 per cent. soap, twenty-three per cent; clay, 22.2 per cent.

In Fig. 5 we have shown slabs covered with the graphite paste similar to that shown in Fig. 1. In this instance the slabs are preferably arranged vertically. They are- In Fig. 6 We have shown a tube coated with the graphite mixture. In this instance the base or tube may be made of porcelain. B indicates collars clamped to the tube and to which the circuit-wires may be connected.

It is obvious that our improvements may be used as a resistance medium as well as for heating purposes.

We claim as our invention- 1. The method herein described of forming an electric heater or resistance, which consists in coating a smooth non-conducting base while heated with a paste containing graphite, clay and water.

2. The method herein described of forming an electric heater or resistance which consists in coating a smooth non-conducting surface while heated with a paste containing graphiite and clay and polishing the coating toharen it.

3. The method herein described of forming an electric heater or resistance which consists in coating a non-conducting base While heated with a paste containing graphite and clay, polishing the coatingv to harden it and then applying subse uent coatings and polishing them until the esired degree of conductivity is obtained.

4. An electric heater or resistance comprising a non-conducting base and a thin even ulnbaked coating containing graphite and c ay.

5. An electric heater or resistance comprising a slab of soapstone and an unbaked coating containing graphite and clay.

6. An electric heater or resistance comprising a non-conducting base and a coating contaming graphite, clay and soap.

7. An electric heater or resistance comprising a slab of soapstone and a coating containing graphite, clay and soap.

8. An electric heater or resistance comprising a slab of soapstone having a smooth surface and a coating thereon of uniform thickness and even distribution containing graphite and clay.

9. An electric heater or resistance comprising a non-conducting base and a thin coating of uniform thickness and even distribution containing graphite, clay and soap.

' 10. An electric heater or resistance comprising a non conducting base having a smooth surface and a series of coatings or layers of a paste containing graphite and clay, each of which layers is polished to harden it and the thickness of the coating being such as to give the required conductivity.

In testimony whereof we have hereunto subscribed our names.

HARMON N. MORSE. JOSEPH C. W. FRAZER. Witnesses: JOHN R. HOOPER, A. J. GRAPE. 

